Why can't java keep up with minecraft?

When I go into one of my servers it lags a heck of allot and then it says that java is not responding?

Guest 07.03.2015

Java has always been incredibly slow. But there could be other reasons why it's not working. Could be slow processor, small amount of RAM, or maybe the server is just incredibly busy serving other requests or processes.

Jeff P 07.03.2015